The combustion of fuels high in sulfur, for example, in conventional middle distillate fuels such as diesel fuel and jet fuel, is considered a serious environmental problem because of its contribution to airborne particulates and acid rain. Governmental regulations have been promulgated that significantly limit the amount of sulfur which may be present in such fuels. Unfortunately, fuels having a suitably low sulfur content in compliance with such regulations may exhibit very poor inherent lubricity, which can lead to problems when the fuel is used. For example, the use of low sulfur-content fuel in diesel engines frequently results in damage to fuel pumps and injectors, which rely on the natural lubricating properties of the fuel to prevent component failure. Therefore, a need has existed to improve the lubricating properties of low sulfur-content fuels to compensate for the loss in lubricating properties associated with reducing the sulfur content.
A number of prior processes have been disclosed for making additives for enhancing various performance characteristics of lubricants and/or combustion fuels in which the additives are based on the reaction products of succinic anhydrides and hydroxyamines.
U.S. Pat. No. 3,272,746 discloses succinimides of long-chain succinic anhydrides (at least 50 carbon atoms) and amines, including hydroxyamines.
U.S. Pat. No. 3,324,033 discloses the reaction product of a high molecular weight succinic anhydride and diethanolamine.
U.S. Pat. No. 3,364,001 discloses the reaction product of an alkenyl succinic anhydride (ASA) and triethanolamine and fuel compositions containing it.
U.S. Pat. No. 3,879,306 describes an automatic transmission fluid which contains a succinamic acid or a mixture of a succinamic acid and a hydroxyalkyl succinimide.
U.S. Pat. No. 4,097,389 teaches succinimides made from C8 to C300 alkenylsuccinic anhydrides and various hydroxyamines. The succinimides are post-treated with a variety of reagents to make them suitable for fuel and lubricant compositions.
U.S. Pat. No. 4,253,876 discloses corrosion inhibitors comprising triesters of an alkenyl or alkyl succinic acid or anhydride and a trialkanolamine.
U.S. Pat. No. 4,325,827 describes hydroxymethyl succinimides and engine oil compositions containing them.
U.S. Pat. No. 4,420,407 describes a lubricating oil composition comprising a mineral oil, overbased calcium sulfonate, and a succinimide made with ethanolamine.
U.S. Pat. No. 4,486,573 discloses acylated hydroxyamines.
U.S. Pat. No. 4,489,194 discloses hydrocarbyl substituted carboxylic acylating agents.
U.S. Pat. Nos. 4,997,456 and 5,122,216 teach succinimides prepared from C12–C30 alkenylsuccinic anhydrides and alkanol polyamines.
U.S. Pat. No. 5,194,068 discloses fuel compositions containing small amounts of an ester of a mono- and/or poly-carboxylic acid with an alkyl alkanolamine or alkyl aminopolyalkylene glycol.
U.S. Pat. No. 6,001,141 describes a low sulfur content fuel composition containing additive compounds including a carboxylic acid substituted by a least one hydroxyl group, derivatives of the carboxylic acid substituted by at least one hydroxy group, and an ester which is the reaction product of a carboxylic acid which does not contain any hydroxy-substitution in the acid backbone and an alkanolamine.
European Patent publication EP 561947 discloses additives which are the reaction products of (1) anhydrides and/or poly-acids, and (2) aminoalcohols or amino/alcohol/amides with long chain hydrocarbyl groups attached used to improve the low-temperature properties of distillate fuels.
European Patent publication EP 632123 describes high-MW (>2000) succinimides containing hydroxyamines as effective diesel fuel dispersants.
Canadian patent publication CA 744,377 discloses succinimides made from high-MW (>700) ASAs and hydroxyamines.
United Kingdom patent publication GB 984,409 describes succinimides prepared from high-MW alkenylsuccinic anhydrides and hydroxyamines.
The disclosures of all the patents noted herein are incorporated herein by reference.
It is desired to provide a lubricity additive for low sulfur-content middle distillate fuels which can compensate for the absence of sulfur therein without impairing the environmental benefit or other desired performance features thereof.